By way of background, the typical remedy for middle ear effusion is a myringotomy, which is a surgical procedure that involves cutting a slit or opening in the tympanic membrane of a patient in order to alleviate a buildup or reduction of pressure in the middle ear cavity and to drain accumulated fluids.
A variety of ear ventilation tubes for insertion into such an opening or slit in the tympanic membrane have been developed. For example, a chronology of middle ear ventilation tubes developed over the years is provided in the article "Middle Ear Ventilation Tubes", by James J. Pappas, M.D. in "The Laryngoscope", 1974.
Frequently the condition of buildup or reduction of pressure in the middle ear cavity, which a ventilation tube is intended to alleviate, requires that the tube remain in place for significant period of time. As discussed in the Pappas article, ventilation tubes have had a variety of configurations and it is also known that such tubes have been made of various materials.
One problem associated with ventilation tubes is clogging over a period of time, which may be caused by epithelial tissue migration, occlusion by middle ear effusions or possibly cerumen (wax) build-up. Tubes made of a polymer such as a fluorocarbon have experienced a relatively low incidence of clogging. However, such tubes will typically extrude from the tympanic membrane within a relatively short time period of, for example, six to nine months. The use of polymer tube is discussed in an article by Karlan et al entitled "Myringotomy Tube Materials: Bacterial Adhesion and Infection" published in the Nov.-Dec. 1980 issue of Otolaryngol Head Neck Surgery.
Vent tubes have also been formed of silicon rubber or other biocompatible materials. One such tube, which includes a fluorocarbon membrane over the outer opening to prevent the passage of liquid but allows air flow, is taught in U.S. Pat. No. 3,916,873. Tissue is prevented from growing over the vent opening by placing an anti-coagulate coating over the membrane. However, even though the membrane is porous it is still subject to clogging easily and does not provide the degree of ventilation of an open tube and does not permit fluid to drain outwardly.
Although vent tubes formed of titanium or titanium alloys have been known to resist extrusion, they have also exhibited the problem of clogging. This significantly reduces the effectiveness of such tubes because many patients require long term ventilation.